It is well known to use a video camera with a computer frame grabber. A typical system employs a video motion camera (such as the CCD 4000 RGB Flash-Sync Camera manufactured by Eastman Kodak Co., Rochester, N.Y.) and a frame grabber board (such as a TARGA.sup.(.TM.) frame store board manufactured by True Vision, Inc., Indianapolis, Ind.) attached to the PC bus of a personal computer. The camera provides the timing to interface with the video frame store board by activating the frame acquire line of the frame store board whenever an external voltage input to the camera is dropped low (e.g., by dropping the "Camera Acquire In" line to the CCD 4000 camera). It is customary to design software to activate the camera's frame acquire line from the computer. To capture an image into the computer in such a customary application, the operator frames the subject while observing the live camera output on a video monitor, and then interacts with the computer keyboard at the proper moment.
Another approach to computer image acquisition is described in U.S. Ser. No. 805,220, entitled "Hand-Manipulated Electronic Camera Tethered to a Personal Computer," which was filed Dec. 11, 1991 in the names of K. A. Parulski, R. H. Hamel, and J. J. Acello, and assigned to the assignee of the present application. In this system an electronic camera is coupled to a personal computer through a computer interface. In particular, a digital interface standard may be used, and images from the camera are input to the computer through a Small Computer System Interface (SCSI). The camera is preferably linked, or tethered, to the computer with a cable, thus allowing a certain amount of mobility for the camera independent of the computer.
Both of these known interfaces have drawbacks. The NTSC signal is an analog signal subject to noise, and additionally requires a special frame grabber card in the computer to decode and digitize the signal. The SCSI signal has a relatively low data rate and a complicated protocol, requiring an expensive SCSI interface integrated circuit in the camera. Notwithstanding such drawbacks, the system described in Ser. No. 805,220 provides a low cost electronic still camera which attaches to a personal computer that provides image processing, storage, and display. By relying on the computer to perform these tasks, the camera cost can be greatly reduced.
A customized high speed bus connection is described in U.S. Pat. No. 4,196,450 for transferring data between a scanner and a specialized processing system. A special architecture is required, including an interprocessor link between a low speed section, having a standard Intel 8080 microprocessor connected to a low speed data bus, and a high speed section having a high speed bus and high speed microprocessor for handling scan data from the scanner. As the scanner is moved across an image page, scan data is supplied to the high speed data bus. Communication between the high speed and the low speed sections is through the interprocessor link. The shortcoming of this arrangement is that a custom computer, including a non-compatible bus, must be built just to handle, process, and store images.
In all of these systems, there is need for a low cost means of digitally interfacing a small camera peripheral to a-portable computer at a rate higher than that provided by a SCSI interface or an RS-232 input, but without the attendant difficulties of either an analog frame grabbing process or a specialized, non-compatible computer architecture.